Find yourself a destroyer carbine and rebarrel and chamber it.
It is cambered for the 9mm largo. Also the extractor will
also need work. I converted one to the 7,62 x 25 works
fine.

The rim dia. for 9mm, 9mm largo and 7.62x25mm are almost exactly the same (9.96 (.392))
5.7x28mm has a tiny little rim: (7.80 mm (0.307 in). which is only slightly larger than 22 rimfires. You'll need to do alot more than just tweak the extractor.

I just converted a Destroyer to 9x19mm. Simple enough. Just took the barrel out and faced the chamber and shoulder back two turns of the threads so I can use the original rear sight. Also shortened to 16 1/2" and threaded for a Gemtech Trinity. I test fired it yesterday. Nice little gun. If I had access to more of them I'd rebarrel one to 7.62x25. Why not?

Was kinda throwing the idea around last night, doing a small amount of research (maybe not enough)...

I was thinking...

If I were to take a .22wmr bolt action rifle, like a Marlin 982 with stainless bull barrel, and granted I could find the right drill bit and a drill press, I think I could build a 5.7x28mm precision rifle!!!

According to Wikipedia (only place I found a good comparison table), the differences I've found were:

Also, the 5.7x28mm has a very steep shoulder angle, which would probably be about right with just a standard .310" drill bit...

Whaddya guys think?

Would a .22wmr bolt catch and hold a 5.7x28, or would I have to increase the diameter by .019? How would I go about doing this?

Does the Marlin 982 have a center-to-rim pin block, or an off-center-to-rim pin block? This is crucial if I'm going to try and cobble the firing pin from a rimfire firing pin block...

I'd probably have to chase the new chamber with another smaller bit to make a pocket for the neck, which could be the 2mm difference between lengths. I haven't looked at a .22wmr up close yet...

Think the .22wmr bull barrel would hold up to the 5.7x28mm chamber pressure?

I think it'd be way neat to have a 5.7x28mm precision rifle, especially if I could cobble a mag adapter that would hold Five-seveN magazines... That'd be later... MUCH later. For now, I'd go with just standard single-shot until I whip up a magazine solution.

What about mags? Would the 7-round 22wmr hold 5.7x28mm? What about the ejector size? Would I have to move it back 2mm to accomodate a longer round, or would it still be able to kick out the 5.7x28mm?

Does anyone have a Marlin 982 in .22wmr and access to a 5.7x28mm round? Or just a .22wmr and 5.7x28mm for visual comparison?

Thanks,
- CK

[edit] Is there anything else I need to know about swapping calibers? Am I underestimating the job? [/edit]

Hi Ceekay,

Cool idea, Don't do it!!!!! At least not with the donor rifle you are looking at now. You will most likely need to do one of the following, if not all:

1. Change the bolt face, most likely you will need to enlarge it slightly if it is not flat faced.
2. Change (meaning fabricate) a new firing pin and extractor.
3. Modify the bolt for new firing pin and extractor.
4. buy a 5.7 chamber reamer, probably both rough and finish reamers. Do not use a drill bit, I am certain that you have nice eyes, and dont want to crude them up with powder burns or brass fragments.
5. Simply hardening the bolt may not do it. In fact, you may be making a huge mistake that will make the bolt more brittle, like really hard glass.
6. I am not intimately familiar with either cartridge you mention in your post, so I am simply conjecturing that the 5.7 uses a slightly more "explosive" powder; maybe faster burning is a better way to describe it. The rifle was designed for an older, perhaps slower burning powder. You may want to review the SAAMI data for both cartriges, and pay special attention to the measurements of pressure. There are chamber pressures, and the rearward pressure, but I can not remember the term for it.

I am not really trying to be a kill-joy, but it just sounds like a non-starter to me. And I like taking risks! That's how I got all of my kids!!!!!